Several thousand people in south-eastern India fled their homes on Wednesday, out of the path of a cyclone due to slam coastal areas after midnight, bringing with it heavy rain.
Nivar, classified as a very severe cyclonic storm, was expected to pack winds of 120 kilometres (75 miles) per hour and gusts of up to 145 km/h when it makes landfall, forecasters said.
Thousands of state and national emergency personnel have been deployed in the southern regions of Tamil Nadu, Andhra Pradesh and Puducherry, where the cyclone was due to hit in the early hours of Thursday morning.
Local authorities have declared a public holiday, shutting everything except emergency services, and a spokesman for the National Crisis Management Committee said thousands had been evacuated from their homes.
Heavy rain was already falling in the region, and was expected to intensify in the next few hours.
Fishermen there were advised not to go out to sea.
More than 110 people died after "super cyclone" Amphan ravaged eastern India and Bangladesh in May, flattening villages, destroying farms and leaving millions without electricity.
But the death toll was far lower than the many thousands killed in previous cyclones of that size, a result of improved weather forecasting and better response plans.